js.bs

5 + 5
You can tell me what this is, right? It’s 10, that’s right.

What about this?

5 + '5'
This is '55'. Makes sense, right?

'5' + 5
This is also '55'. This makes more sense than the last one, though, even though it still makes no sense.

5 + +'5'
Now what’s this? This is 10 again.

'5' - - '5'
This is also 10.

NaN === NaN
This is false.

{} + []   === 0
[] + []   === ''
[] * 1    === 0
false + 1 === 1
These are all true.

typeof NaN === 'number'
true! JavaScript, you’ve been exposed.

This is just what I can think of off the top of my head. JavaScript can be so confusing. It’s not just type juggling you have to worry about. Also, speaking of type juggling:

5    == '5'
[]   == ''
({}) == '[object Object]'
true. This is why you should always use ===. == is just plain useless, I assure you. I don’t know why it exists.